One objective is to further purify, characterize, and study the mechanism of action of glutathione-organic nitrate ester reductase (GSH-ONER), a specific enzyme in the metabolism of glycerol trinitrate, etc. Preliminary work has suggested more than one enzyme, catalyzing the type reaction: 2 GSH plus R-ONO2 yields GSSG plus HNO2 plus HNO2 plus R-OH. The study will involve purification, crystallization, search for prosthetic groups, characterization of the protein, and mechanism of reaction with substrates. The reaction is an oxidation-reduction distinct from nitro and inorganic nitrate reductases. The possible role of metal, disulfide, trisulfide, or persulfide (S) groups in the enzyme are important because of known non-enzymatic and enzymatic GSH reactions. GSH-ONER may be a selenium containing protein like glutathione peroxidase. A second objective is to compare GSH-ONER with the GSH-S-transferases, a group of 5-6 enzymes which are of great interest because of their specificity for GSH and the remarkable variety of reactions they catalyze. Jakoby et al. find that several of them have some GSH-ONER activity, but possible identity with our guinea pig GSH-ONER remains to be determined, as we have 7 x greater specific activity. A third objective is to examine in much greater detail the nature and specificity of GSH-dependent enzymes catalyzing a number of reactions in prostaglandin synthesis and metabolism. In liver we find two, possibly three, GSH-peroxidases, and Nugteren has recently reported the remarkable observation that GSH-S transferases can catalyze several endoperoxidase, endoperoxide ismerase, and endoperoxide reductase reactions. Attack by GSH-ONER is highly correlated with vasodilator potency in organic nitrates. Highly purified enzyme would make possible later immunochemical studies to determine possible similarity to receptor groups in smooth muscle. A selective inhibitor for liver GSH-ONER would be a very useful drug for prolonging the anginal relieving action.